1. Field of the Invention
The present invention relates generally to ophthalmic lenses, and more specifically to toric ophthalmic lenses such as tonic contact lenses, corneal inlays, and intraocular lenses.
2. Description of the Related Art
Ophthalmic lenses, such as spectacles and contact lenses, may be configured to provide both spherical and cylinder power. The cylinder power of a lens is used to correct the rotational asymmetry aberration of astigmatism of the cornea or eye, since astigmatism cannot be corrected by adjusting the spherical power of the lens alone. Lenses that are configured to correct astigmatism are commonly referred to as tone lenses. As used herein, a toric lens is characterized by a base spherical power (which may be positive, negative, or zero) and a cylinder power that is added to the base spherical power of the lens for correcting the astigmatism of the eye.
Tone lenses typically have at least one surface that can be described by an asymmetric tone shape having two different curvature values in two orthogonal axes, wherein the tonic lens is characterized by a “low power meridian” with a constant power equal to the base spherical power and an orthogonal “high power meridian” with a constant a power equal to the base spherical power plus the cylinder power of the lens. Intraocular lenses, which are used to replace or supplement the natural lens of an eye, may also be configured to have a cylinder power for reducing or correcting astigmatism of the cornea or eye.
In addition to astigmatism, the cornea or eye may also have other higher order aberrations that can degrade optical quality or visual acuity. For example, so called third order, or Seidel, aberrations also include spherical aberration and coma, in addition to astigmatism. As discussed in U.S. Patent Application Number 2009/0279048, which is herein incorporated by reference in its entirety for all purposes as if fully set forth herein, these additional higher order aberrations may be reduced or corrected by introducing an aspheric surface or shape that is characterized by a curvature and conic constant. The aspheric surface may be on the same surface or opposite surface to that of the tonic shape. Thus, the combination of the tone and aspheric shapes provides the possibility of reducing or correcting all third order aberrations of lens itself and/or of cornea or eye.
One problem that has yet to be implemented in to ophthalmic lens design is that the cornea or eye may introduce even higher order aberrations, for example, fifth-order, seventh-order, and ninth-order aberrations. Furthermore, because the cornea may generally have an asymmetric surface shape, the value of these aberrations may vary over different meridians. However, it may be useful to approximate this complexity of the typical cornea by characterizing the higher order aberrations as having different values in orthogonal axes, for example, along the high and low power meridians. While the magnitude of such higher order aberrations may be relatively small compared to third-order or Seidel aberrations, a clinically significant treatment may be provided by correcting these aberrations. Fifth and higher order aberrations cannot generally be reduces by ophthalmic lens surfaces characterized by only a curvature and conic constant. Rather, additional lens or surface design parameters are necessary.
Another problem within the art of ophthalmic lens design is that of identifying average amounts of various aberrations within different populations. Different cornea models have been developed that provide average curvature and conic constant values for populations of human eyes, for example, as disclosed in U.S. Pat. No. 6,609,793, which is herein incorporated by reference in its entirety for all purposes as if fully set forth herein. However, the average spherical aberrations within such populations can vary depending on other variables such as the amount astigmatism, axial length of the eye, average corneal curvature, age, sex, ethnicity, and the like. For example, a subgroup within the population all having about 1 Diopter of astigmatism may have a different amount of spherical aberrations, on average, than another subgroup within the population all having about 3 Diopters of astigmatism. In addition, the average conic may be different between the high and low power meridians, either for the population as a whole or for different subgroups within the population having different amounts of astigmatism or differentiated by some other parameter(s).
Yet another problem may occur in the case of subjects that have previously undergone a corneal refractive procedure, such as LASIK or PRK, and now need or desire to have the natural lens replaced by an intraocular lens. In such cases, the corneal refractive procedure may have been performed on only the central portion of the cornea, for example, out to a diameter of 3 millimeters or 4 millimeters. The border between the treated and untreated portions of the cornea may have relatively discontinuous or large changes in curvature and/or power, which in turn may introduce fifth and higher order aberrations that are different from those in a typical population that has not received a corneal refractive procedure.
For these and other reasons, there is a need for ophthalmic lenses, and methods of design and implementation thereof; that take into account fifth and higher order aberrations of individual, corneas and average corneas representative of a population of eyes. There is also a need for ophthalmic lenses, and methods of design and implementation thereof; that take into account changes in the average aberrations of populations of eyes over changes in certain parameters, such as differing amounts of astigmatism.